Performance and application investigation of a hybrid surface-subsurface flow constructed wetland for in-situ water purification in small-micro rivers

Small-micro rivers, characterized by low water volume, poor mobility, and limited self-purification capacity, face significant eutrophication risks from non-point source pollution. Conventional ex-situ treatment methods are often costly and maintenance-intensive. This study introduces an in-situ hybrid constructed wetland that combines surface flow and subsurface flow processes, utilizing the natural topography of small-micro rivers to enable multi-directional water movement without lifting facilities. After stable operation, microbial analysis indicated enrichment of functional microorganisms involved in nitrogen and phosphorus metabolism, such as Dechloromonas (3.2–5.0 %) and Hyphomicrobium (1.0–1.7 %). The system achieved removal loads of 1.22 ± 0.13 g/(m²·d) for NH4+−N and 0.11 ± 0.02 g/(m²·d) for TP, significantly reducing eutrophication and enhancing self-purification capacity. Operationally, it requires no electricity or material consumption, with maintenance limited to periodic replanting of aquatic vegetation and substrate cleaning, resulting in low construction (approximately 820 CNY/m²) and operational costs. This approach provides an eco-friendly and economical solution for improving regional ecological health and offers practical guidance for rehabilitating similar small-micro water bodies.